I think the difference between sardines and Spanish mackerel is as follows:

1. Different genera: sardines belong to the family Herringidae of the order Herring, while Spanish mackerel belongs to the family Perciformes.

2. Different appearance: Sardines are longer, slightly flattened on the sides, round in the abdomen, with a smaller head and a notochord in the tail. The Spanish mackerel has a long body, flat sides, a pointed and long head, and no notochord in the tail.

3. Different nutritional values: Sardines are rich in protein, vitamins, minerals and other nutrients, and are suitable for pregnant women, parturient women, the elderly and other people. Bay mackerel is rich in unsaturated fatty acids, protein, vitamins, calcium, iron and other nutrients.

4. The meat texture is different: the meat of sardines is delicious, while the meat of Spanish mackerel is loose and easy to chew.